1. Field of the Invention
The present invention relates to a novel catalyst component for polymerizing .alpha.-olefins. More particularly, the present invention relates to a catalyst component for polymerization which makes possible the production of an industrially useful .alpha.-olefin polymer, a catalyst for polymerizing an .alpha.-olefin with the catalyst component, and a process for preparing an .alpha.-olefin polymer with use of the catalyst.
2. Background Art
As the homogeneous catalysts for polymerizing .alpha.-olefins, there is known the so-called Kaminsky catalyst. This type of the catalyst has an extremely high activity and a narrow molecular weight distribution, and it is also characterized in that a polymer having a narrow distribution of a monomer composition is obtained in copolymerization.
Transition metal compounds used in the preparation of .alpha.-olefin polymer with the Kaminsky catalyst is classified roughly into those types of non-crosslinked and crosslinked ligands.
As the typical example of the non-crosslinked complex, there is disclosed biscyclopentadienylzirconium dichloride in Japanese Patent Laid-Open Publication No. 19309/1983, but this catalyst seems to have a drawback that when ethylene-1-hexene copolymer is prepared at a polymerization temperature of a practical level, increased content of hexene leads to decrease in the molecular weight whereby the polymer species obtainable thereby may be limited.
As the typical examples of the crosslinked complex, there are disclosed ethylene-1,2-bis(1-indenyl)zirconium dichloride and ethylene-1,2-bis(1-(4,5,6,7-tetrahydroindenyl))zirconium dichloride in Japanese Patent Laid-Open Publication No. 130314/1986, but these compounds also seem to have a drawback which is similar to that in the non-crosslinked complex. It has also been proposed for the crosslinked complex to change its substituent structure so as to make the complex suited for the production of an .alpha.-olefin polymer having a high molecular weight in Japanese Patent Laid-Open Publication Nos. 268307/1992 and 268308/1992. The catalysts so modified do not appear to have improved performance at elevated temperatures which are economically advantageous.
All of these crosslinked complexes have a structure that a crosslinking group is directly linked to a five-membered ring in the ligand, and no examples of syntheses of the complex in which the crosslinking group is bonded to the portion other than the five-membered ring have been reported insofar as the present inventors know.
The object of the present invention is to provide a novel catalyst component for polymerizing an .alpha.-olefin which makes possible the production of an industrially useful .alpha.-olefin polymer in a high yield, a catalyst for polymerizing an .alpha.-olefin, and a process for producing an .alpha.-olefin polymer.